Utilization of 1-oxa-2,2-(dimesityl)silacyclopentane acetals in the stereoselective synthesis of polyols

We have developed a route for the stereoselective synthesis of 1-oxa-2,2-(dimesityl)silacyclopentane acetals, intermediates in the synthesis of highly functionalized 1,3-diols. This route involves a diastereoselective conjugate addition reaction of a hydrosilyl anion, a subsequent diastereoselective enolate alkylation, and a fluoride-catalyzed intramolecular hydrosilylation reaction to afford the oxasilacyclopentane acetal. A highly selective nucleophilic substitution reaction, followed by oxidation of the C-Si bond, leads to the desired polyol.     

Production of oxygen enriched air by rapid pressure swing adsorption

A novel rapid pressure swing adsorption (RPSA) process is described for production of 25–50% oxygen enriched air. The embodiment consists of one or more pairs of adsorbent layers contained in a single adsorption vessel. The layers undergo simultaneous pressurization-adsorption and simultaneous depressurization-purge steps. A total cycle time of 6–20 seconds is used. The process yields a very large specific oxygen production rate and a reasonable oxygen recovery for production of 20–50 mole% oxygen enriched gas.It is demonstrated by a simple mathematical model of isothermal single adsorbate pressure swing ad(de)sorption concept on a single adsorbent particle that the specific production rate of a PSA process cannot be indefinitely increased by reducing the cycle time of operation when adsorbate mass transfer resistances are finite.     

Determination of the quaternary compound ciclotropium in human biological material after hydrolysis and derivatization with the fluorophor flunoxaprofen chloride

The quantitative determination of the quaternary spasmolytic compound ciclotropium and its metabolite N-isopropyltropinium is described for human plasma and urine. The analytical procedure consists of ion-pair extraction from biological material, alkaline hydrolysis, subsequent derivatization with the fluorophor flunoxaprofen chloride and separation by high-performance liquid chromatography on a reversed-phase column with fluorimetric monitoring. The detection limits of 0.5 ng/ml in plasma and 10 ng/ml in urine at signal-to-noise ratios higher than 3 permit the determination of pharmacokinetic parameters after therapeutic doses.     

Optimal double-configuration study of the lowest excited Π states of H2

Various levels of approximation (Hartree-Fock, configuration interaction and double-configuration Hartree-Fock method) are compared for extensive and limited exponent optimization of the atomic orbitals of the wavefunctions. The potential energy curves for the lowest-lying ¹ _u, ³ _u, ¹ _g, ³ _g states of the hydrogen molecule are presented. The shapes of the curves on the highest level of approximation, i.e. with the optimal double-configuration wavefunction, are basically in agreement with previous, more sophisticated and time-consuming work. The influence of the various approximations is also studied for several one-electron properties: charge distribution of the wavefunction along and perpendicular to the molecular axis, quadrupole moment and core attraction energy distribution. Differences arise to the work of Zemke et al. [1], who used a limited exponent optimization with a larger basis set, in the _g states where the orbitals are very diffuse. The differences concern magnitude and location of minima and maxima of potential curves, as well as considerable changes in one-electron properties which depend strongly on the spatial distribution of the orbitals.

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Zusammenfassung Verschiedene Approximationsstufen (Hartree-Fock, Konfigurationenwechselwirkung und Doppelkonfigurationen-Hartree-Fock-Methode) werden für ausgedehnte und begrenzte Exponentenoptimisierung von Atomorbitalen der Wellenfunktionen verglichen. Die Potentialkurven für die niedrigsten ¹ _u, ³ _u, ¹ _g, ³ _g Zustände des Wasserstoffmoleküls werden angegeben. Die Form der Kurven im Rahmen der besten Näherung, d. h. mit Doppelkonfiguration, stimmen im wesentlichen mit früheren aufwendigeren Rechnungen überein. Der Einfluß der verschiedenen Approximationen wird auch an einigen Einelektroneneigenschaften studiert: Ladungsverteilung der Wellenfunktion längs und senkrecht zur Molekülachse, Quadrupolmoment und Verteilung der Rumpfenergie. Unterschiede erscheinen zur Arbeit von Zemke et al. [1], die einen größeren Basissatz mit begrenzter Optimisierung verwandten, bei den _g Zuständen, wo die -Orbitale sehr diffus sind. Die Unterschiede betreffen Größe und Lage der Minima und Maxima der Potentialkurven sowie beträchtliche Änderungen in solchen Einelektroneneigenschaften, die stark von der räumlichen Verteilung der Orbitale abhängen.

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Résumé Comparaison de différents niveaux d'approximation (Hartree-Fock, interaction de configuration et Hartree-Fock à deux configurations) pour des optimisations étendues et limitées des orbitales atomiques de base. Calcul des courbes d'énergie potentielle pour les plus bas états ¹ _u, ³ _u, ¹ _g, ³ _g de la molécule d'hydrogène. Pour la fonction d'onde la plus raffinée: H.F. à deux configurations, la forme des courbes est en accord avec les résultats obtenus dans des travaux précédents plus complexes et plus coûteux. On étudie aussi l'influence des diverses approximations sur plusieurs propriétés monoélectroniques: distribution de charge le long de l'axe moléculaire et perpendiculairement à celui-ci, moment quadrupolaire et distribution de l'énergie d'attraction de coeur. On trouve des différences avec le travail de Zemke et al. (1), qui utilisent une plus grande base partiellement optimisée, pour les états _g où les orbitales sont très diffuses. Les différences concernent la grandeur et la position des extrema des courbes de potentiel, ainsi que des variations importantes des propriétés monoélectroniques qui dépendent fortement de la distribution spatiale des orbitales.

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On leave to: Institut für Theoretische Chemie, Universität Stuttgart.

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On leave to: Office of Computing Activities, National Science Foundation, Washington, D.C.     

Cyclopentadienyl ruthenium, rhodium, and iridium vertices in metallaboranes: geometry and chemical bonding

Most cyclopentadienylmetallaboranes containing the vertex units CpM (M = Co, Rh, Ir; Cp = eta(5)-cyclopentadienyl ring, mainly eta(5)-Me(5)C(5)) and CpRu donating two and one skeletal electrons, respectively, have structures closely related to binary boranes or borane anions. Smaller clusters of this type, such as metallaborane analogues of arachno-B(4)H(10) (e.g., (CpIr)(2)B(2)H(8)), nido-B(5)H(9) (e.g., (CpRh)(2)B(3)H(7) and (CpRu)(2)B(3)H(9)), arachno-B(5)H(11) (e.g., CpIrB(4)H(10)), B(6)H(6)(2)(-) (e.g., (CpCo)(4)B(2)H(4)), nido-B(6)H(10) (e.g., CpIrB(5)H(9) and (CpRu)(2)B(4)H(10)), and arachno-B(6)H(12) (e.g., (CpIr)(2)B(4)H(10)), have the same skeletal electron counts as those of the corresponding boranes. However, such clusters with eight or more vertices, such as metallaborane analogues of B(8)H(8)(2)(-) (e.g., (CpCo)(4)B(4)H(4)), arachno-B(8)H(14) (e.g., (CpRu)(2)B(6)H(12)), and nido-B(10)H(14) (e.g., (CpRu)(2)B(8)H(12)), have two skeletal electrons less than those of the corresponding metal-free boranes, analogous to the skeletal electron counts of isocloso boranes relative to those of metal-free deltahedral boranes. Some metallaboranes have structures not analogous to metal-free boranes but instead analogous to metal carbonyl clusters such as 3-capped square pyramidal (CpRu)(2)B(4)H(8) and (CpRu)(3)B(3)H(8) analogous to H(2)Os(6)(CO)(16) and capped octahedral (CpRh)(3)B(4)H(4) analogous to Os(7)(CO)(21). In the metallaborane structures closely related to metal-free boranes, the favored degrees of BH and CpM vertices appear to be 5 and 6, respectively.     

Viscosity of confined inhomogeneous nonequilibrium fluids

We use the nonlocal linear hydrodynamic constitutive model, proposed by Evans and Morriss [Statistical Mechanics of Nonequilibrium Liquids (Academic, London, 1990)], for computing an effective spatially dependent shear viscosity of inhomogeneous nonequilibrium fluids. The model is applied to a simple atomic fluid undergoing planar Poiseuille flow in a confined channel of several atomic diameters width. We compare the spatially dependent viscosity with a local generalization of Newton's law of viscosity and the Navier-Stokes viscosity, both of which are known to suffer extreme inaccuracies for highly inhomogeneous systems. The nonlocal constitutive model calculates effective position dependent viscosities that are free from the notorious singularities experienced by applying the commonly used local constitutive model. It is simple, general, and has widespread applicability in nanofluidics where experimental measurement of position dependent transport coefficients is currently inaccessible. In principle the method can be used to predict approximate flow profiles of any arbitrary inhomogeneous system. We demonstrate this by predicting the flow profile for a simple fluid undergoing planar Couette flow in a confined channel of several atomic diameters width.     

J Aggregation of Thiacarbocyanine in Aqueous Gelatin Solutions

The aggregation processes of 3,3′-disulfopropyl-4,4′,5,5′-dibenzo-9-ethylthiacarbocyanine betaine were studied in aqueous gelatin solutions. Gelatin molecules were shown to favor the formation of J aggregates from dye dimers according to the block mechanism. Acidic gelatins much stronger favor J aggregation of the dye than alkaline and, especially, modified gelatins. High contents of microgels and high-molecular-mass fractions in gelatin retard the formation of long-wavelength aggregates.     

Mössbauer investigation of the reaction between HCl and tin dopant ions located on the surface of Cr2O3 microcrystals

The chemical behavior of surface-located tin dopant ions depends strongly on their valence state. At room temperature all Sn(II) ions readily react with gaseous hydrogen chloride while, under similar conditions, the predominant part of Sn(IV) ions is not affected by this gas. The results of this study, along with those previously obtained for both valence states of tin dopant exposed to a H₂S atmosphere, suggest that lower reactivity of Sn(IV) ions is essentially due to their higher coordination number and concomitant steric hindrance effects.     

Optimization of the Aerosol Filter Parameters

Theoretical approach to the optimization of the parameters of two-stage fibrous aerosol filter is reported. The approach is based on earlier developed method for the calculation of the clogging of model filter where the particle deposit is approximated by the porous shell on the fibers. The values of optimal fiber radii are determined from the condition of maximal dust capacity of a filter at given limiting pressure drop and total initial efficiency. Optimization was performed with allowance for possible variation in the prefilter thickness.     

Using IMAP technology to identify kinase inhibitors: comparison with a substrate depletion approach and analysis of the nature of false positives

IMAP is a fluorescence polarisation-based assay method which can be applied to the measurement of protein kinase activity. Using a model serine/threonine kinase we found that IMAP generated a good assay window (Z' > 0.8), was very tolerant of DMSO, and was flexible with respect to sample processing (stopped reactions were stable over a period of several days). Using a set of six low molecular weight inhibitors of the kinase, we found a good correlation between IMAP and scintillation proximity assay (SPA) potency data. IMAP, which measures product accumulation, was compared in an HTS setting with a substrate depletion method (luminescence-based measurement of ATP concentration). There was a reasonable (approximately 50%) overlap in primary hits from a 17,000 compound set, but more apparent false positives were generated from the IMAP method. We followed up the compounds that showed activity in the IMAP method but not in the luminescence assay. Approximately 10% of these compounds displayed intrinsic fluorescence, suggesting that they were false actives by virtue of intrinsic spectroscopic properties. Compound activity by competition of phosphopeptide binding to IMAP beads can occur with high concentrations of chelating compounds, but did not occur with any of the false actives, suggesting that this form of interference is rare.